(a) Field of the Invention
The present invention relates to a heat exchange-type reactor, and more particularly, to a heat exchange-type reactor used to produce acrylic acid by utilizing a catalytic oxidation reaction.
(b) Description of the Related Art
Acrylic acid is typically produced from propylene that has undergone a two-stage vapor phase catalytic oxidation reaction. In the first stage, molecular oxygen, diluted inert gas, steam, and a predetermined amount of a catalyst to oxidize propylene to thereby produce acrolein is used. In the second step, molecular oxygen, diluted inert gas, vapor, and a predetermined amount of a catalyst to oxidize acrolein is again used to thereby produce acrylic acid.
A reactor performing these processes is configured to perform both stages in a single device or to perform the two stages in two different devices. U.S. Pat. No. 4,256,783 discloses such a reactor.
In industries that use such reactors, much effort is being put forth to increase manufacturing productivity by improving the structure of the reactor, providing an optimal catalyst to bring about the oxidation reaction, or by improving the driving of the processes, etc. In this regard, a space velocity of propylene supplied to the reactor or the concentration of the propylene is increased. In either of these two cases, the oxidation reaction in the reactor abruptly occurs such that it is difficult to control the reaction temperature, and in addition, many hot spots are generated in catalyst layers of the tubular reactor such that by-products such as carbon monoxide and carbon dioxide are produced to thereby reduce the yield of the acrylic acid. Further, when producing acrylic acid that uses a high space velocity and a high concentration of propylene, the accelerated exothermic reactions cause difficulty in controlling reaction temperature. As a result, a problem with the catalyst layer occurs (e.g., a reduction in the number of active sites caused by a breakaway of effective elements and a sintering of metal elements) such that its function deteriorates.
Hence, during the manufacture of acrylic acid, controlling the heat in the reactor is the most important aspect for ensuring high productivity. In particular, it is necessary to minimize temperatures at the hot spots in the catalyst layers and heat accumulation in the vicinity of the hot spots, and to eliminate runaway of the reactor caused by the hot spots (runaway is a situation in which the heat generation reaction becomes excessive so that the reactor cannot be controlled or the reactor explodes).
To remedy such problems, U.S. Pat. No. 4,256,783 is structured such that a shield plate is mounted in a shell of a reactor that provides a plurality of tubes. The shield plate divides the space within the shell such that the temperature in the resulting separate spaces may be controlled according to different temperature distributions.
In addition to the above patent, configurations to obtain effective cooling systems are disclosed, in which molten salt circulation paths for the mounting of various baffles (e.g., U.S. Pat. No. 3,871,445), and an oxidation reactor design that combines a cooler and a heat exchanger (e.g., U.S. Pat. No. 3,147,084) are provided.
However, in such reactors, although the management of hot spots in the catalyst layers by the shield plate is more effectively realized, since a separate heat exchanger is required for each of the divided spaces in the shell, the overall structure of the device becomes more complicated.